System and method for detecting seat occupancy in a vehicle

ABSTRACT

A system for determining seat occupancy in a motor vehicle includes a microwave transmitter, a microwave receiver and preferably a reflector. If a person is between those appliances, the microwave radiation is attenuated. The reflector can be a backscattering device, such that the radiation received by the receiver is unequivocally associated with the reflector. Furthermore or alternatively, the transit time of the microwaves can be measured, to be subsequently processed in combination with an analysis of the seated position of passengers. In preferred embodiments, the microwave radiation diffraction properties around an object are also used to obtain the seated position of passengers. The determination of a seat occupancy and optionally of seat occupancy mode can be advantageously used for locking or on the other hand releasing an airbag.

BACKGROUND OF THE INVENTION Field of the Invention

The invention relates to a system for detecting seat occupancy in avehicle, said system comprising at least one microwave transmitter, atleast one reflector and at least one microwave receiver, the at leastone microwave transmitter, the at least one reflector and the at leastone microwave receiver being disposed such that between the at least onemicrowave transmitter and the at least one microwave receiver aradiation path is provided which is divided into at least one firstradiation path and at least one second radiation path, such thatmicrowave radiation emitted from the at least one microwave transmittercan reach, via the at least one first radiation path, the at least onereflector at least when the seat is unoccupied and such that microwaveradiation reflected by the at least one reflector can reach, via the atleast one second radiation path, the at least one microwave receiver andsuch that, depending on the seat occupancy, an object can be located inthe first radiation path and/or the second radiation path so that theradiation received by the microwave receiver can be influenced dependingon the seat occupancy.

The invention also relates to a system for detecting seat occupancy in avehicle, said system comprising at least one microwave transmitter andat least one microwave receiver, the at least one microwave transmitterand the at least one microwave receiver being disposed such thatmicrowave radiation emitted by the at least one microwave transmittercan reach, via a radiation path, the at least one microwave receiver atleast when the seat is unoccupied and such that, depending on the seatoccupancy, an object can be located in the radiation path so that theradiation received by the microwave receiver can be influenced dependingon the seat occupancy.

The invention relates furthermore to a method for detecting seatoccupancy in a vehicle, said method comprising the steps: emission ofmicrowave radiation, reflection of the emitted microwave radiation andreceiving of the reflected microwave radiation, whereby a radiation pathis provided which is divided into at least one first radiation path andat least one second radiation path, the emitted microwave radiationtravels via the at least one first radiation path, the reflectedmicrowave radiation travels via the at least one second radiation pathand an object can be located, depending on the seat occupancy, in thefirst radiation path and/or the second radiation path, so that thereceived radiation can be influenced depending on the seat occupancy.

The invention also relates to a method for detecting seat occupancy in avehicle, said method comprising the steps: emission of microwaveradiation and receiving of microwave radiation, wherein the emittedmicrowave radiation travels via a radiation path and, depending on theseat occupancy, an object can be located in the radiation path so thatthe received radiation can be influenced depending on the seatoccupancy.

Systems and methods of this type are known. They serve in particular toinfluence the activation behavior of an airbag depending on seatoccupancy.

An example of such a system and method is known from U.S. Pat. No.6,199,904 B1. Here, microwaves are transmitted by a microwavetransmitter to a reflecting structure in a vehicle seat. The reflectedmicrowaves are recorded by a microwave receiver. Since the intensity ofthe reflected microwaves depends on whether the microwave radiation isattenuated by a person who is occupying the seat, conclusions can bedrawn from the result of the evaluation as to seat occupancy. Adisadvantage of the system and method, however, is that the airbagcontrol is not always based on reliable evaluations. For example, it canbe possible for reflection to occur on objects other than thosereflection objects provided for the purpose in the seat. This wouldsimulate the result that the seat was not occupied, which could resultin the airbag being locked. This can have life-threatening consequencesfor the occupants of the vehicle. Furthermore, the calibrations requiredas part of the configuration process are very expensive, which drives upthe cost of the system. Furthermore, all additional evaluations involvecomputing time, which would stand in the way of dynamic measurement,that is measurement only in the event of a vehicle impact.

SUMMARY OF THE INVENTION

The object of the invention is to provide a system and a method whichovercome the disadvantages of the prior art and which in particularenable reliable and cost-effective detection of seat occupancy.

This object is achieved in the features of the independent claims.

Advantageous embodiments of the present invention are described in thedependent claims.

The invention builds upon the generic system which is fitted with areflector in that the at least one reflector 12 is a modulatingbackscattering device or a non-modulating backscattering device, wherebyin the latter case the signal transit time is determined in the receiverin order to establish from which reflector the received signaloriginates. Modulation of the microwave radiation by the backscatteringdevice makes it possible for the reflector to be readily distinguishedfrom other metallically conductive objects. If, for example, reflectionof the microwave radiation occurs on the casing of a laptop which thepassenger in a car is working on, then this will not lead to the systemassuming that the seat is unoccupied. An airbag would therefore triggerin the event of an impact.

The terms “reflector, reflect, etc.” are used in the context of thepresent disclosure in a very general sense. Not only reflection in thetraditional sense is meant but also, for example, the return ofelectromagnetic radiation by means of a modulating or non-modulatingbackscattering process.

The invention builds furthermore upon the generic system in that thepath between microwave transmitter and microwave receiver covered by themicrowave radiation can be determined by measurement of the transittime. It is possible by this means to determine the setting of the seat.The distance between transmitter and reflector can also be determined bymeasurement of the transit time and the received signal thus assigned tothe reflector. Information is in this way also available for airbagcontrol.

It is particularly useful in this connection that the position of a seatcan be determined and that, from the result of determination of the pathand from the result of determination of the position of the seat, it canbe determined whether the radiation received by the microwave receiverhas traveled via the radiation path between microwave transmitter andmicrowave receiver. Such plausibility considerations are basicallyunnecessary where a backscattering device is used as a reflector but cannonetheless be used for redundancy purposes. The considerations areparticularly useful because of the transit time of the microwavesignals, however, if no pattern is stamped on the reflected microwaveradiation, for example, by a backscattering process. It can then beestablished by means of additional analysis of the position of the seatwhether the reflection may stem, for example, from a reflector in theseat rest or whether the reflection originates from a laptop on thepassenger's lap.

It can furthermore be useful in the system according to the inventionfor the at least one microwave transmitter and the at least onemicrowave receiver to be disposed spatially separated. The separatearrangement of microwave transmitter and microwave receiver makes itpossible for a system to be implemented without a reflector. Forexample, the microwave transmitter can be disposed in the roof or on thedashboard, while the microwave receiver is located in the back rest of aseat. This arrangement is in contrast to the prior art, in which alarge-area reflection in the seat was used in order to reflect theemitted microwave radiation to the transmitter.

It is particularly advantageous if the backscattering device is amodulating backscattering device. By means of the pattern stamped bymodulation, the reflected signal can be uniquely assigned to areflector.

The system according to the invention is further developed in anadvantageous manner in that the at least one microwave transmitter andthe at least one microwave receiver are implemented as at least onemicrowave transmitting and receiving device with a transmitting and areceiving antenna.

The microwave radiation thus goes from the microwave transmitting andreceiving device via the first radiation path to the reflector and backfrom the reflector via the second radiation path to the microwavetransmitting and receiving device, the at least one first radiation pathand the at least one second radiation path thus being essentiallyidentical. The microwave transmitting and receiving device may, forexample, be located in the dashboard of the vehicle. If the reflector ismounted in the back rest of the seat to be monitored, then the course ofthe beam of the emitted and of the reflected microwave radiation will,where applicable, pass through the upper body region of a passenger. Ifa person is sitting properly on the seat, then he/she will cover thereflector, and the receiving antenna will receive a level approximatelysix orders of magnitude lower than when the person is not present. Wherethe antenna is disposed in the dashboard or in the cockpit and thereflector is disposed in the seat back rest, it can even be detected ifa person is not in a proper seated position. If the person is inclinedforward, then a proportion of the emitted microwave radiation can reachthe reflector through diffraction of the microwave radiation around thebody. This typical pattern is communicated to the airbag system whichthen evaluates whether the airbag can still be activated, i.e. when theinclination is limited, or whether no activation should still takeplace, i.e. in the case of a marked inclination. The arrangement of theantenna in the cockpit and of the reflector in the back rest likewisemeans that, for example, a child seat can be transported safely on thefront passenger seat. The bulk of the microwave radiation will passunimpeded to the reflector and back from this to the receiver, so thatthe activation of an airbag can be prevented, since the child seat willin general be made of plastic and the radiation will be damped only bythe body of the child.

As an additional safety measure, it is possible to mount a furtherreflector on the child seat. In this way, microwave radiation whichwould otherwise have been absorbed in the child seat or in the childsitting in the child seat will also be reflected. Activation of theairbag can thus be prevented even more reliably. If modulatingbackscattering devices are used as reflectors, then the backscatteringdevices in the seat rest or on the child seat can modulate the signalsdifferently so that it can be detected unambiguously that a child seatis located on the seat.

It is particularly useful that a control unit is provided which,depending on the radiation received by the microwave receiver, triggers,locks or releases functions in the vehicle. The detection of seatoccupancy can also be appropriate in connection with other functions inthe vehicle, but the release or locking of an airbag is a particularlyimportant achievement of the present invention.

This can for example also be fashioned such that the at least onereflector is an electrically conductive foil. Such a foil can beincorporated in a simple manner into the back of a seat, with virtuallyno additional installation space being needed and virtually noadditional weight being added.

The system according to the invention can be further developed byimplementing the backscattering device as a passive, semipassive,semiactive or active backscattering device. Passive backscatteringdevices are constructed particularly simply, need no additional energysupply and insofar provide a particularly cost-effective solution.Semipassive backscattering devices are operated with an additionalamplifier which takes a small amount of electrical power. They have theadvantage compared with passive backscattering devices that they canreflect with higher intensity. More reliable evaluations can be carriedout on this basis. An active backscattering device, that is abackscattering device with active electronic components, would carry outa particularly reliable evaluation. This enables particularly reliableevaluation due to increased microwave intensities. However, due to themicrowave radiation, the loading on the vehicle passengers is higher inthis embodiment of the present invention than in the case of passivebackscattering devices. The semiactive backscattering device is similarto the semipassive backscattering device, but exhibits amplification ofthe signal to be reflected.

The system according to the invention can be further developed in aparticularly advantageous manner in that the at least one microwavetransmitter and/or the at least one microwave receiver are integralcomponents of an access control and ignition system installed in thevehicle. In microwave-based access control and ignition systems, theantenna for covering the interior is generally located in such aposition that it can also respond to reflectors disposed in the vehicleseats. Consequently, the embodiment of the present invention, whereincomponents of the access control and ignition system are used fordetecting seat occupancy, can provide an integrating and thuscost-reducing measure.

For comparable reasons, it can be advantageous for the evaluation of thesignals received by the microwave receiver to be supported or carriedout by means which are deployed as part of an access control andignition system installed in the vehicle.

It can furthermore be useful for several differently modulatingbackscattering devices to be provided. These can be mounted, forexample, at different heights in the seat back rest. If these reflectorsare encoded differently, then in addition to the basic detection of seatoccupancy, the size of the passenger and his/her position on the seatcan be detected. This information can be taken into account for examplewhen an airbag is activated or when several airbags in differentpositions are activated.

The system according to the invention is advantageously fashioned suchthat the at least one first radiation path and/or the at least onesecond radiation path follow a straight-line route. When talking of aradiation path following a straight-line route in the present context,then this refers to the propagation of the radiation excludingdiffraction phenomena. The present remarks consequently relate to thegeometric arrangement of the components. With no object in the radiationpaths, there are therefore direct lines of sight between transmitter,reflector and receiver. A particularly simple system is provided in thisway.

It can, however, also be useful for the at least one first radiationpath and/or the at least one second radiation path to follow aroundabout route. The microwave radiation can be guided through thevehicle by means of conductive materials used in the vehicle such thatcertain zones can be selectively illuminated without additionalmicrowave transmitting and receiving devices being required.

The system according to the invention is further developed in aparticularly advantageous manner in that the position of the object inthe radiation path influences the intensity received by the microwavereceiver on the basis of the diffraction of microwaves around the objectand in that the intensity received by the microwave receiver providesinformation about the position of the object. Since microwave radiation,in contrast to infrared radiation, for example, can, due to itswavelength, exhibit marked diffraction phenomena at an object disposedin the radiation path, it is possible to make use of the changes inintensity due to diffraction effects. For example, the leaning forwardof a person on a seat can be detected if, in so doing, this person onthe one hand adequately shields a reflector disposed in the seat base,but on the other hand exposes a reflector disposed in the back rest insuch a manner that microwaves diffracted around the object can reach thereflector. An empty seat can thus be distinguished from a seat occupiedby an adult and also for example from a seat occupied by a child with achild seat, since in the latter case diffraction to a reflector disposedin the seat base can also occur due to the position of the child beingraised by the child seat.

The invention builds furthermore on the generic method, in which emittedmicrowave radiation is reflected, firstly in that the reflection iseffected by means of a backscattering process.

The advantages and special features of the systems according to theinvention are implemented on the basis of these inventive methods. Thisalso applies to the particularly preferred embodiments of the inventivemethods specified below.

On the one hand, the invention builds alternatively or additionally onthe generic method in that the path covered by the microwave radiationis determined by measurement of the transit time.

Furthermore, the method according to the invention preferably providesthat the position of a seat is determined and that, from the result ofdetermination of the path and from the result of determination of theposition of the seat, it is determined whether the radiation receivedhas traveled via the radiation path.

It is furthermore advantageously provided in the method according to theinvention that the at least one microwave transmitter and the at leastone microwave receiver are disposed spatially separated.

It is particularly advantageous if the backscattering process is amodulating backscattering process.

The method according to the invention is in particular further developedin an advantageous manner in that the at least one first radiation pathand the at least one second radiation path are identical.

It is particularly useful for functions in the vehicle to be triggered,locked or released depending on the radiation received by the microwavereceiver.

The method according to the invention can, for example, also befashioned such that an electrically conductive foil is used forreflecting.

The method according to the invention can be further developed in thatthe backscattering process is implemented by a passive, a semipassive, asemiactive or an active backscattering process.

The method according to the invention can be further developed in aparticularly advantageous manner in that the emitting and/or thereceiving is/are carried out on the basis of an access control andignition system installed in the vehicle.

For comparable reasons, it can be advantageous for the evaluation ofreceived signals to be supported or carried out by means which aredeployed as part of an access control and ignition system installed inthe vehicle.

Furthermore, it can be useful for the backscattering process to becarried out by several differently modulating backscattering devices.

The method according to the invention is advantageously fashioned suchthat the at least one first radiation path and/or the at least onesecond radiation path follow(s) a straight-line route.

It can, however, also be useful for the at least one first radiationpath and/or the at least one second radiation path to follow aroundabout route.

The method according to the invention can further be developed in aparticularly advantageous manner such that the position of the object inthe radiation path influences the received intensity on the basis of thediffraction of the microwaves around the object and such that thereceived intensity provides information about the position of theobject.

The invention is based upon the recognition that particularly reliableand yet simple and cost-effective detection of seat occupancy can beprovided by deploying a backscattering device, in particular amodulating backscattering device, as a reflector. The certainty of thesystem can also be improved by checking the place of reflection of themicrowave radiation through a separately determined seated position onthe basis of transit time measurements. Furthermore, microwave radiationdiffraction phenomena can be used in an advantageous manner. Due to theconsiderable but not complete absorption of microwave radiation in thehuman body, there are advantages in using microwave radiation bycomparison with using other wave forms, for example ultrasound, laserradiation or light and infrared radiation. Microwave radiation travelsindependently of pressure, temperature, brightness and otherenvironmental conditions. The method of measurement is very fast due tothe simplicity of the evaluation, so that dynamic measurement, forexample only in the event of an impact, is possible. Further advantagesof the invention are that detection of seat occupancy can be carried outat very high speed. The time for the recording can lie, for example, inthe millisecond range. It is possible by this means to lend airbagcontrol a dynamism which makes it for example possible even after anairbag has been triggered to influence the filling of the airbagdepending on the seat occupancy or the position/inclination of theperson on the seat, preferably through reduction of pressure.

BRIEF DESCRIPTION OF THE DRAWING

The invention will now be explained, using particularly preferredembodiments as examples, with reference to the accompanying drawings, inwhich:

FIG. 1 shows a preferred embodiment of a system according to theinvention;

FIG. 2 shows the embodiment according to FIG. 1 with a person in a firstseated position;

FIG. 3 shows the embodiment according to FIG. 1 with a person in asecond seated position;

FIG. 4 shows the embodiment according to FIG. 1 with a seat occupied bya baby seat;

FIG. 5 shows a further preferred embodiment of a system according to theinvention with a first person;

FIG. 6 shows the embodiment according to FIG. 5 with a second person;

FIG. 7 shows a sectional view from above of the arrangement shown inFIG. 6.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the description below of preferred embodiments of the presentinvention, the same reference symbols designate the same or comparablecomponents.

FIG. 1 shows a preferred embodiment of a system according to theinvention. A microwave transmitting and receiving device 10 is disposedin the dashboard or in the cockpit 24 of a vehicle. A reflector 12which, depending on the embodiment, can be fashioned as a modulatingbackscattering device or as a simple electrically conductive foil(non-modulating backscattering device), is arranged in a back rest 26.The seat 20 can be displaced in the usual manner, it being particularlypreferred if the position of the seat 20 can be determined.

Microwave radiation is emitted from the microwave transmitting andreceiving device 10 towards the reflector 12. This microwave radiationis reflected by the reflector 12 and thus sent back to the microwavetransmitting and receiving device 10. The reflection through thereflector 12 can take place in a conventional manner, if the reflector12 is a simple electrical conductive film for example.

The reflection 12 can, however, also occur as part of a modulatingbackscattering process, a code being imprinted on the reflectedradiation, for example through modulation. To this end, the reflector 12can be fashioned as a passive, semipassive, semiactive or activebackscattering device.

In a control unit 22, the signals emitted by the reflector 12 can beevaluated with regard to distance (signal transit time), level andquality.

In the situation shown in FIG. 1, no person is located on the seat 20.The reflected signal is therefore received with a high level and a highquality.

Besides the embodiment comprising a reflector 12 in the seat 20, it isalso possible to implement the present invention without using areflector. In this case, a microwave receiver can be disposed in theseat 20, for example at the point where the reflector 12 is positionedin FIG. 1. In a further embodiment, these positions of receiver andreflector can also be swapped. These principles also apply to theembodiments of the present inventions shown below.

FIG. 2 shows the embodiment according to FIG. 1 with a person in a firstsitting position. In this representation, a person 14 is sittingproperly on the seat 20. The person covers the reflector 12. For thisreason, the microwave transmitting and receiving device 10 receives asignal which is many orders of magnitude, for example six orders ofmagnitude, smaller than when the seat is unoccupied. In this case,activation of the airbag can be released so that said airbag activatesin the event of an impact.

FIG. 3 shows the embodiment according to FIG. 1 with a person in asecond sitting position. The person 16 shown here is inclined forward.If the upper body is to a sufficient degree in front of the reflector12, then a sufficient intensity can again be transmitted from themicrowave transmitting and receiving device to the reflector 12 and viceversa, from the reflector to the microwave transmitting and receivingdevice. The intensity can be used to detect the angle of inclination ofthe person. As of a certain angle of inclination, activation of theairbag is not appropriate because of head injuries; this is referred toas the out-of-position case. If the reflector and the out-of-positioncase are detected, activation of the airbag can be prevented. Thecritical angle of inclination, as of which the out-of-position case isdetected, can be adjusted depending on the wavelength, level orintensity, reflector area, mounting of reflector and microwave sendingand receiving device, evaluation algorithm, etc.

FIG. 4 shows the embodiment according to FIG. 1 with a seat occupied bya baby seat. Here, a baby is located in a child seat, in the presentcase in a so-called reboard seat 18. This seat is secured properly tothe passenger seat 20. Due to the relative positions of microwavetransmitting and receiving device 10, reflector 12 and reboard seat 18,only limited damping of the microwave radiation takes place.Consequently, activation of the airbag is prevented. In addition, it ispossible and possibly very useful to fasten a reflector to the back ofthe reboard seat 18. In this way, the situation with child seat 18 onthe seat 22 can be distinguished from the situation with no object onthe seat 20, for example by means of special modulation of the microwaveradiation by this reflector.

If in the system according to the invention the reflector 12 is shieldedfor example by a metal object, this results in more intense reflection.The intensity of this reflection may possibly lie in the same order ofmagnitude as the intensity of reflection by the reflector 12. There arenow a variety of possible ways in which the control unit 22 can detectthe different situations. If the reflector is a modulatingbackscattering device with unique encoding, then the reflection by theshading metal object is uniquely detected on this basis. Reflection by ashielding metal object can alternatively or additionally be detected onthe basis of a signal transit time measurement, particularly if thetransit time is compared with the actual seated position, which can bedetermined by an additional sensor.

It is also advantageous for objects having little or no electricalconductivity in front of the reflector 12 only to shield the reflectorslightly. The signals received by the control unit therefore correspondto the “empty seat” position, so that activation of the airbag iscorrectly locked.

FIG. 5 shows a further preferred embodiment of a system according to theinvention with a first person. In this exemplary embodiment, tworeflectors 12 are built into the vehicle seat 20. A reflector 12 isdisposed in the back rest 26; a further reflector 12 is disposed in theseat base 28. The control unit 22 with microwave transmitting andreceiving device 10 is disposed in the roof control unit 30 of avehicle.

When an adult person 14 is sitting properly on the seat, he/she coversthe reflectors 12, and the control unit 22 receives a level severalorders of magnitude lower than when the seat 20 is empty. To thisextent, the system as per FIG. 5 operates in a comparable way to thesystems described in connection with FIGS. 1 to 4. However, since anadditional reflector 12 is now disposed in the seat base 28, the forwardinclination of the person 14 can be detected with greater reliability.In this case, the person 14 namely exposes the reflector 12 so thatmicrowave radiation, at least due to diffraction phenomena, can find itsway between the microwave transceiver 10 and the reflector 12 in theback rest 26. The reflector 12 in the seat base 28, by contrast, isstill completely covered by the person 14 so that this can be used asadditional information indicating that this is a person leaning forward14 and not an empty seat 20.

FIG. 6 shows the embodiment as per FIG. 5 with a second person. On thebasis of the system according to the invention, the situation shown herecan also be distinguished from that of an adult person leaning forward,as was explained with reference to FIG. 5. A child 32 is sitting on achild seat 34 which is disposed on the seat 20. Also disposed in theseat 20 are two reflectors 12, one in the back rest 26 and one in theseat base 28. Because of the child seat 34, which in general absorbs themicrowaves very much less than the body of the child 32, microwaves, duein particular to their diffraction properties, can find their waybetween microwave transceiver 10 and the reflectors 12 in the back rest26 and the seat base 28. The reflector 12 in the seat base 28 thereforereceives a greater intensity than it could receive if an adult personwere sitting directly on the seat base 28.

Thus, through appropriate arrangement of several reflectors 12 andcommensurate appropriate arrangement of the microwave transceiver 10,different situations can be detected with regard to seat occupancy inthe vehicle.

FIG. 7 shows a sectional view from above of the arrangement shown inFIG. 6. The section in FIG. 7 is along the plane marked A in FIG. 6.Various paths are shown by which microwave radiation can reach thereflector 12 in the back rest 26, assuming the situation of a child 32on a child seat 34. Firstly, there is the direct path 36 betweenmicrowave transmitter/receiver 10 and the reflector 12 which in thepresent situation is shielded by the child 32. Due to the distancebetween the child 32 and the reflector 12 which is maintained in eachcase by the child seat 34, microwaves can, however, also often pass fromthe microwave transceiver 10 to the reflector 12 and in the reversedirection on indirect paths 38, for example as a result of diffractionaround the body and as a result of reflection or scattering. This isimpeded only immaterially by the child seat 34 since, compared with thehuman body, it has a very much lower absorption capacity.

The invention can be summarized as follows. A system for detecting seatoccupancy in a vehicle comprises a microwave transmitter 10, a microwavereceiver 10 and preferably a reflector 12. If a person is locatedbetween these objects, then the microwave radiation is attenuated. Thereflector 12 can be a modulating backscattering device, such that theradiation received by the receiver can be unequivocally associated withthe reflector 12. If the reflection is not modulated, then a measurementof the transit time of the microwave radiation is carried out and thistransit time processed further, possibly in combination with an analysisof the seated position of passengers. In preferred embodiments, it isprovided that the microwave radiation diffraction properties around theobject also be used to obtain further information about the seatedposition of passengers. The determination of whether and, if applicable,how a seat is occupied can advantageously be used for locking or forreleasing an airbag.

The features of the invention disclosed in the above description, in thedrawings and in the claims may be essential, both individually and inany combination, to practical implementation of the invention.

1. A system for determining seat occupancy in a vehicle, comprising: atleast one microwave transmitter, a plurality of reflectors stationarilydisposed in predetermined locations at a seat of the vehicle, and atleast one microwave receiver, commonly arranged: to define between saidmicrowave transmitter and said microwave receiver a radiation pathdivided into at least one first radiation path and at least one secondradiation path; wherein microwave radiation emitted by said microwavetransmitter can reach at least one of said reflectors along the at leastone first radiation path when the seat is unoccupied; wherein themicrowave radiation, after reflection by said at least one reflector canreach said microwave receiver via the at least one second radiationpath; wherein, depending on the seat occupancy, an object may be locatedin at least one of the first radiation path and the second radiationpath and the radiation received by the microwave receiver may beinfluenced in dependence on the seat occupancy; and wherein saidreflectors are modulating backscattering devices.
 2. The systemaccording to claim 1, wherein said at least one microwave transmitterand said at least one microwave receiver are disposed spatially separatefrom one another.
 3. The system according to claim 1, wherein: said atleast one microwave transmitter and said at least one microwave receiverare implemented in at least one microwave transmitting and receivingdevice comprising a transmitting and receiving antenna; and the at leastone first radiation path and the at least one second radiation path areidentical.
 4. The system according to claim 1, which comprises a controlunit configured to selectively trigger, block, or enable functions inthe vehicle depending on the radiation received by said microwavereceiver.
 5. The system according to claim 1, wherein said reflectorsare formed of electrically conductive foil.
 6. The system according toclaim 1, wherein said reflectors are backscatter devices selected fromthe group consisting of passive devices, semi-passive devices,semi-active devices, and active devices.
 7. The system according toclaim 1, wherein said at least one microwave transmitter and/or said atleast one microwave receiver are components of an access control andignition system of the vehicle.
 8. The system according to claim 1,wherein the signals received by said microwave receiver are processedfor evaluation with means used in an access control and ignition systeminstalled in the vehicle.
 9. The system according to claim 1, whereinsaid reflectors are differently modulating backscattering devices. 10.The system according to claim 1, wherein the first and second radiationpaths follow a straight line.
 11. The system according to claim 1,wherein the at least one first radiation path and/or the at least onesecond radiation path follow a roundabout route.
 12. The systemaccording to claim 1, wherein: a position of the object in the radiationpath influences an intensity of a signal received by said microwavereceiver due to a diffraction of microwaves about the object; and theintensity of the received signal provides information about the positionof the object.
 13. A method of determining seat occupancy in a vehicle,which comprises the following steps: defining a radiation path with atleast one first radiation path and at least one second radiation path;emitting microwave radiation to propagate along the at least one firstradiation path; reflecting the microwave radiation from a definedlocation at the seat of the vehicle with a modulating backscatteringprocess to form reflected microwave radiation, and causing the reflectedradiation to propagate along the at least one second radiation path;receiving the reflected microwave radiation; and determining a seatoccupancy and deducing whether or not an object is located in at leastone of the first radiation path and the second radiation path, where theradiation received by a microwave receiver is influenced depending onthe seat occupancy.
 14. The method according to claim 13, whichcomprises placing the at least one microwave transmitter and the atleast one microwave receiver spatially separate from one another. 15.The method according to claim 13, wherein the at least one firstradiation path and the at least one second radiation path are identical.16. The method according to claim 13, which comprises selectivelytriggering, locking, or releasing functions in the vehicle in dependenceon the radiation received.
 17. The method according to claim 13, whichcomprises reflecting the radiation with an electrically conductive foil.18. The method according to claim 13, which comprises implementing thebackscattering process with a passive, a semi-active, a semi-passive, oran active backscattering device.
 19. The method according to claim 13,which comprises emitting and/or receiving with an access control andignition control system installed in the vehicle.
 20. The methodaccording to claim 13, which comprises carrying out or supporting anevaluation of the received signals within a framework of an accesscontrol and ignition system installed in the vehicle.
 21. The methodaccording to claim 13, which comprises effecting the backscatteringprocess with a plurality of differently modulating backscatteringdevices.
 22. The method according to claim 13, wherein the at least onefirst radiation path and/or the at least one second radiation pathfollow a straight-line route.
 23. The method according to claim 13,wherein the at least one first radiation path and/or the at least onesecond radiation path follow a roundabout diversion route.
 24. Themethod according to claim 13, wherein a position of the object in theradiation path influences an intensity of a received signal due to adiffraction of microwaves; and the method comprises deducing informationabout the position of the object from the intensity of the receivedsignal.